# RSP vs SPY: Why These S&P 500 ETFs Track Differently

The S&P 500 dominates American investing. Two popular ETFs track it: SPY (SPDR S&P 500 ETF Trust) and RSP (Invesco S&P 500 Equal Weight ETF). Over the past 20 years, their returns have diverged sharply. Understanding why matters for your portfolio.

SPY uses market-cap weighting. This means larger companies get larger positions. Apple, Microsoft, Nvidia, and Tesla command outsized influence. When these giants rise, SPY soars. When they stumble, SPY stumbles harder. This concentration has turbocharged returns during the artificial intelligence boom and the tech rally of recent years.

RSP takes the opposite approach. It assigns equal weight to each S&P 500 company. Apple gets the same 0.2% allocation as a mid-cap industrial stock. This forces RSP to constantly rebalance, selling winners and buying laggards. Mechanically, it locks in gains from outperformers and accumulates stakes in underperformers.

Over two decades, SPY has crushed RSP. The math is simple: the largest companies have delivered the best returns. The Magnificent Seven stocks (Apple, Microsoft, Google, Amazon, Tesla, Nvidia, Meta) account for an enormous slice of S&P 500 gains in recent years. SPY owns them at massive weights. RSP owns them at tiny weights.

SPY's 20-year annualized return significantly exceeds RSP's. The gap widens in tech-driven years and narrows during periods when smaller cap stocks outperform. The 2024 market environment, dominated by mega-cap AI plays, favors SPY dramatically. Equal weighting works best when performance spreads evenly across company sizes. That hasn't happened.

Expense ratios barely differ. SPY charges 0.03% annually. RSP charges 0.20% annually. The 0.17 percentage point gap compounds over decades but doesn't fully explain the return split. The real culprit is market structure and company dominance.

Investors chase SPY for good reason. It delivers core S&P 500 exposure without the drag of constant rebalancing. Its market-cap weighting aligns with economic reality. The most valuable companies tend to stay valuable. Owning them in proportion to their market value captures the winners.

RSP appeals to rebalancing enthusiasts and those who distrust mega-cap concentration. Equal weighting forces discipline: buy the beaten-down, sell the beloved. Academic studies suggest rebalancing adds return over time through disciplined selling of winners. The catch is that rebalancing cost and tracking error often eliminate the benefit, especially when mega-cap stocks keep winning.

For most savers, SPY remains the cleaner choice. Its minimal fees and straightforward exposure to the market's actual weightings simplify investing. If you believe the Magnificent Seven will face headwinds and smaller companies will lead the next cycle, RSP offers hedging against concentration risk. Just know you'll pay for that hedge in fees and likely underperformance if mega-cap dominance continues.

The 20-year lesson is clear: the S&P 500's top holdings have driven returns. Weighting them accordingly has paid off.